Typical bituminous emulsions contain coal tar or asphalt, mineral colloids, water and additives. In coal tar emulsions, the coal tar composes approximately 35% of the emulsion. It is principally used due to its ability to protect against gasoline, kerosene and oil spills. It also imparts the desired black color when cured. The mineral colloids compose approximately 15% of a coal tar emulsion. Preferably, the mineral colloids are clays such as a ball clay or an attapulgite clay. These so-called "colloidal clays" have many of the chemical and physical properties necessary to suspend the bitumen in the aqueous phase, providing the emulsion with the consistency and stability desired.
In asphalt emulsions, asphalt composes up to approximately 50% of the emulsion. The clay composes up to approximately 30% of such an emulsion.
Additionally, fillers may be added. These fillers may be defined as bulking agents which stabilize the composition after application, or fibers which may absorb the aqueous phase and/or provide reinforcing properties. Such fillers are also added for economy, shrinkage control, to impart anti-skid properties to the final coating product and increase wear or durability of the final coating product. Examples of such fillers include sand, mica, ground slate, diatomaceous earth, ground limestone, wollastonite, perlite, cellulose fibers, talc, ground coal slag, and synthetic fibers. Fillers are typically added as needed to provide the desired bulking and gel properties for the emulsion composition.
It has also been common to include additives in the emulsions to improve the performance of the emulsions. These additives can be used to provide various results, including decreasing curing times, enhancing color of the cured film, increasing or improving the suspension of fillers, improving weatherability, improving gasoline, oil and chemical resistance, improving resistance to trafficking and water, improving filler bonding and providing longer lasting films.
The additives currently on the market to improve the suspension and bonding of fillers are primarily latex/polymer additives including acrylonitrile butadiene based polymers, neoprenes and vinyl acetates. These additives are normally sold to the contractor market through the manufacturer of the emulsion. Commonly, the contractor will dilute the coal tar emulsion with water and add the recommended level of additive to this diluted emulsion. This addition of water and additive is either done at the contractor's home office or at the job site. The emulsion is then either sprayed, squeegeed, or roller applied to the surface to be coated.
A number of significant problems stem from the use of these latex/polymer additives. While such additives may improve the suspension of sand in the emulsion they remain water susceptible in the cured coating. Because these latex/polymer additives remain water susceptible they are easily re-emulsified when applied on damp surfaces or when in contact with water prior to or after fully being cured. This results in poor traffic resistance, easy removal of the coating, peel up of the coating, overall poor wear resistance and release of the filler component of the coating.
These failures are of major concern as many of these coatings are applied to damp surfaces or are exposed to moisture, particularly rainfall prior to or after being fully cured. These coatings are often used on airport pavement where the problems associated therewith result in damage to plane engines and overall safety concerns due to lack of coating durability and skid resistance.
Another problem associated with latex/polymer additive modified bituminous emulsions of the prior art is the possibility of shocking the emulsion upon addition of the latex/polymer additive. Such a shock results in agglomeration and uneven distribution of the additive--the additive floats to the surface and creates localized thickening. To avoid the problem of shocking the emulsion, it is necessary to dilute the additives of the prior art with water prior to addition to the emulsion. Such a procedure requires time consuming additional steps.
Additionally, the additives of the prior art can become expensive to use in such emulsions. Traditionally, manufacturers suggested the use of 2 to 4 gallons of latex additive per 100 gallons of coal tar emulsion concentrate and 30 to 50 gallons of water. Additionally, 300 to 500 pounds of silica sand is commonly added to these emulsions. Such a large amount of additive increases the cost of the overall coating. Further, in order to provide a "thicker" coating and give better wear resistance manufacturers of latex additives have been recommending that the sand loading in the emulsion be increased with a corresponding increase in latex additive. Such increased sand loading and increased use of the latex additives has resulted in even worse failure of such coatings because of the increased latex additive which is water susceptible.
In summary, a considerable number of drawbacks and problems exist in the art relating to clay-stabilized bituminous emulsions. There is a need for an improved emulsion composition resulting in a coating exhibiting improved resistance to trafficking and water and improved cohesion.